Collaboration Teams - Members share responsibility for posting refined answers to the guided readings - succinct, relevant, clear, and with pictures or a video to compliment.
When contributing to the reading guide, follow these steps: 1) First complete the reading guide on your own from the cells unit page. 2) Write your response to a question in word and then copy it. Be sure to upload pictures and/or video for each question. 3) Click on the edit button and then go to the appropriate question and paste your answer below it.Sign your contribution with your first name and last initial and TEAM COLOR 4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Then click Save.
Blue
Purple
Green
Pink
Yellow
Orange
Red
16-19
14-15, 20
11-13
9-10, 21
6-8,
4-5,
1-3,
Cell Membrane Dynamics!
1. What does selective permeability mean and why is that important to cells? Selective permeability is a property of biological membranes that allows some substances to cross more easily than others. It is important because it allows the cell to uptake nutrients and also to secrete waste. It also allows the cell to keep all of its essential parts and molecules in while still allowing certain outside molecules to enter. –Jackie H. Red Team
This dotted line represents a selectively permeable membrane because only the water molecules can fit through the spaces while the molecules of the other substance are too large to fit through. Kim K. Red Team
2. What is an amphipathic molecule? An amphipathic molecule is molecule that has both a hydrophilic region and a hydrophobic region. –Jackie H. Red Team
The phosphilipid bilayer of the cell membrane has both hydrophilic heads and hydrophobic tails making it amphipathic. Kim K. Red Team
3. What were the ideas concerning the plasma membrane models below:
a.Gorter and Grendel Gorter and Grendel reasoned that cell membranes must actually be phospholipid bilayers. They also stated that double layers of molecules could exist as a stable boundary between two aqueous compartments because the molecular arrangement protects the tails of the phospholipids from water and exposes the heads. –Jackie H. Red Team
Gorter and Grendel determined that this structure made up the phospholipid bilayer. Kim K. Red Team
b.Davson and Danielli Davson and Danielli suggested that the difference between the heads and tails of phospholipids could be accounted for if the membrane was coated on both sides with hydrophilic proteins. –Jackie H. Red Team
Kim K. Red Team
c.Singer and Nicolson Singer and Nicolson proposed that membrane proteins are dispersed and individually inserted into the phospholipid bilayer, with only their hydrophilic regions protruding far enough from the bilayer to be exposed to water. –Jackie H. Red Team
Singer and Nicolson determined that the cell membrane was a fluid mosaic with proteins despersed throughout it, like this picture. Kim K. Red Team
4. Describe the freeze fracture technique and why is it useful in cell biology.
General outline of technique:
1. Cells are quickly frozen in liquid nitrogen, which immobilizes cell components instantly.
2. Block of frozen cells is fractured. This fracture is irregular and occurs along lines of weakness like the plasma membrane or surfaces of organelles.
3. Surface ice is removed by a vacuum (freeze etching)
4. A thin layer of carbon is evaporated vertically onto the surface to produce a carbon replica.
5. Surface is shadowed with a platinum vapor.
6. Organic material is digested away by acid, leaving a replica.
7. Carbon-metal replica is put on a grid and examined by a transmission electron microscope.
The freeze fracture technique is particularly useful for examining lipid membranes and their incorporated proteins.
Dan
5. How is the fluidity of cell membrane’s maintained?
The phospholipid bilayer ensures a membrane’s fluidity. Unsaturated hydrocarbon tails have kinks that keep the molecules from packing together, enhancing membrane fluidity. Dan
6. Label the diagram below – for each structure – briefly list it’s function:
Cholesterol = reduces membrane fluidity at moderate temperatures but hinders solidification of phospholipids at low temperatures Integral proteins= penetrate the hydrophobic core of the lipid bilayer Peripheral proteins= appendages loosely bound to the surface of the membrane Glycolipid= molecules that are formed by a covalent bond between carbohydrates and lipids Glycoprotein= molecules formed by a covalent bond between carbohydrates and proteins Membrane carbohydrates= important in helping cells recognize other cells, so that there can be sorting of cells into tissues and organs, and rejection of foreign cells Fibers of extracellular matrix= attached to certain membrane proteins on the exterior or the cell which gives animals cells a stronger framework than the plasma membrane itself could provide Microfilaments of cytoskeleton= may be bonded to membrane proteins which helps maintain cell shape and stabilizes the location of certain membrane proteins
7. List the six broad functions of membrane proteins. 1. Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and extracellular matrix
8. How do glycolipids and glycoproteins help in cell to cell recognition?
Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane. Some membrane carbohydrates are then attached to lipids, creating glycolipids. Also, some are covalently bonded with proteins to create glycoproteins. Since they are now linked to the interior side of the cell membrane, they can now interact with the surface molecules of other cells.
9. Why is membrane sidedness an important concept in cell biology? Membrane sidedness is an important concept in cell biology because a lot of important components of a cell are contained inside of the cell. It is important for us to understand which side of the membrane these actions are taking place in.
Steve W.
10. How has our understanding of membrane permeability changed since the discovery of aquaporins? We now understand that the passage of water molecules through the cell membrane is facilitated by aquaporins, which are channel proteins specific to water. -Amanda
11. What is diffusion and how does a concentration gradient relate to passive transport?
Diffusion is the movement from high concentrations to low concentrations.A substance will travel to lower concentrations on it concentration gradient until it has reached equilibrium.Passive transport is a movement across the cell without any energy being used. THE CONCENTRATION GRADIENT ITSELF REPRESENTS POTENTIAL ENERGY; THIS IS THE DRIVING FORCE OF DIFFUSION.
Martin A
13. Why is free water concentration the “driving” force in osmosis?
Free water concentration is the diffusion of water from a lower solute concentration across the membrane to a high solute concentration
-Adam A
14. Why is water balance different for cells that have walls as compared to cells without walls? A cell w/o a wall is in an isotonic envirornment meaning there will be no net movement of water across the plasma membrane. Water flows across the membrane but at the same rate in both direction. A cell w/ walls is turgid when healthy meaning its very firm w/ alot of water.
-Steph A
15. Label the diagram below:
Lysed Normal Shriveled Turgid Flaccid Plasmolyzed
a) animal cell fairs best in an isotonic environment unless it has spacial adaptations to offset the osmotic uptake or loss of water
b) plant cells are turgid & generally healthiest in hypotonic environment, where uptake of water is eventually balanced by elastic wall
-Sawyer & Steph, but mostly Sawyer 16. What is the relationship between ion channels, gated channels and facilitated diffusion – write 1 -2 sentences using those terms correctly.
Facilitated diffusion is the phenomenon in which polar molecules and ions can move through the cell membrane with the help of transport proteins. Ion channels and gated channels are two examples of such transporter proteins.
In this image their is a higher concentration of a substance outside of the membrane and it is diffusing through by passive transport. No energy is used just the concentration of substance is enough. It moves through gated and ion channels.
~Ilian D 17. How is ATP specifically used in active transport? In active transport, energy is needed to transport a molecule across the membrane against the gradient. ATP serves as the source of energy in this process. ATP provides this energy by transferring one of its phosphate groups onto the intracellular side of the transporter protein. Binding of the phosphate causes a conformational change in the protein.
~Ilian D
18. Define and contrast the following terms: membrane potential, electrochemical gradient, electrogenic pump and proton pump. Membrane potential is the voltage across a membrane, the result of the separation of opposite charges.
Electrochemical gradient is a combination of two forces on an ion: the first one is chemical force (the ion’s concentration gradient), the second one is an electrical force (the result of the membrane potential).
An electrogenic pump is a transport protein that generates voltage across a membrane by transporting more ions in one direction than the other. A proton pump is the most common electrogenic pump in plants, bacteria and fungi, and it is responsible for pumping protons from the inside of the cell to the extracellular environment.
An electrogenic pump generates a membrane potential, and the membrane potential leads to an electrochemical gradient. ~Ilian D
19. What is cotransport and why is an advantage in living systems? Cotransport is a mechanism in which a single ATP-powered pump that transports a specific solute indirectly drives the active transport of several other solutes. This provides an advantage to living systems because it allows cells to take up critical nutrients such as sugars and amino acids against a concentration gradient. The sugars and amino acids can enter the cell when they ‘hitch’ a ride with a proton.
The hydrogen getting pumped out by ATP causes the transport of hydrogen back into the membrane with the addition of sucrose because sucrose is needed with hydrogen to pump through.
~Ilian D
20. What is a ligand?
A ligand is any molecule that binds specifically to a receptor site of another molecule.
- Laura C
21. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated endocytosis.
Collaboration Teams - Members share responsibility for posting refined answers to the guided readings - succinct, relevant, clear, and with pictures or a video to compliment.
When contributing to the reading guide, follow these steps:
1) First complete the reading guide on your own from the cells unit page.
2) Write your response to a question in word and then copy it. Be sure to upload pictures and/or video for each question.
3) Click on the edit button and then go to the appropriate question and paste your answer below it. Sign your contribution with your first name and last initial and TEAM COLOR
4) Scroll to the very bottom and in the Optional comment box, place a summary of what you did and sign it (e.g. "I answered chp 26 question 3" - Tom S.) Th en click Save.
Cell Membrane Dynamics!
1. What does selective permeability mean and why is that important to cells?
Selective permeability is a property of biological membranes that allows some substances to cross more easily than others. It is important because it allows the cell to uptake nutrients and also to secrete waste. It also allows the cell to keep all of its essential parts and molecules in while still allowing certain outside molecules to enter. –Jackie H. Red Team
2. What is an amphipathic molecule?
An amphipathic molecule is molecule that has both a hydrophilic region and a hydrophobic region. –Jackie H. Red Team
3. What were the ideas concerning the plasma membrane models below:
a. Gorter and Grendel
Gorter and Grendel reasoned that cell membranes must actually be phospholipid bilayers. They also stated that double layers of molecules could exist as a stable boundary between two aqueous compartments because the molecular arrangement protects the tails of the phospholipids from water and exposes the heads. –Jackie H. Red Team
b. Davson and Danielli
Davson and Danielli suggested that the difference between the heads and tails of phospholipids could be accounted for if the membrane was coated on both sides with hydrophilic proteins. –Jackie H. Red Team
c. Singer and Nicolson
Singer and Nicolson proposed that membrane proteins are dispersed and individually inserted into the phospholipid bilayer, with only their hydrophilic regions protruding far enough from the bilayer to be exposed to water. –Jackie H. Red Team
4. Describe the freeze fracture technique and why is it useful in cell biology.
General outline of technique:
1. Cells are quickly frozen in liquid nitrogen, which immobilizes cell components instantly.
2. Block of frozen cells is fractured. This fracture is irregular and occurs along lines of weakness like the plasma membrane or surfaces of organelles.
3. Surface ice is removed by a vacuum (freeze etching)
4. A thin layer of carbon is evaporated vertically onto the surface to produce a carbon replica.
5. Surface is shadowed with a platinum vapor.
6. Organic material is digested away by acid, leaving a replica.
7. Carbon-metal replica is put on a grid and examined by a transmission electron microscope.
The freeze fracture technique is particularly useful for examining lipid membranes and their incorporated proteins.
Dan
5. How is the fluidity of cell membrane’s maintained?
6. Label the diagram below – for each structure – briefly list it’s function:
Cholesterol = reduces membrane fluidity at moderate temperatures but hinders solidification of phospholipids at low temperatures
Integral proteins= penetrate the hydrophobic core of the lipid bilayer
Peripheral proteins= appendages loosely bound to the surface of the membrane
Glycolipid= molecules that are formed by a covalent bond between carbohydrates and lipids
Glycoprotein= molecules formed by a covalent bond between carbohydrates and proteins
Membrane carbohydrates= important in helping cells recognize other cells, so that there can be sorting of cells into tissues and organs, and rejection of foreign cells
Fibers of extracellular matrix= attached to certain membrane proteins on the exterior or the cell which gives animals cells a stronger framework than the plasma membrane itself could provide
Microfilaments of cytoskeleton= may be bonded to membrane proteins which helps maintain cell shape and stabilizes the location of certain membrane proteins
7. List the six broad functions of membrane proteins.
1. Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and extracellular matrix
8. How do glycolipids and glycoproteins help in cell to cell recognition?
Cells recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane. Some membrane carbohydrates are then attached to lipids, creating glycolipids. Also, some are covalently bonded with proteins to create glycoproteins. Since they are now linked to the interior side of the cell membrane, they can now interact with the surface molecules of other cells.
9. Why is membrane sidedness an important concept in cell biology?
Membrane sidedness is an important concept in cell biology because a lot of important components of a cell are contained inside of the cell. It is important for us to understand which side of the membrane these actions are taking place in.
Steve W.
10. How has our understanding of membrane permeability changed since the discovery of aquaporins?
We now understand that the passage of water molecules through the cell membrane is facilitated by aquaporins, which are channel proteins specific to water. -Amanda
11. What is diffusion and how does a concentration gradient relate to passive transport?
Diffusion is the movement from high concentrations to low concentrations. A substance will travel to lower concentrations on it concentration gradient until it has reached equilibrium. Passive transport is a movement across the cell without any energy being used. THE CONCENTRATION GRADIENT ITSELF REPRESENTS POTENTIAL ENERGY; THIS IS THE DRIVING FORCE OF DIFFUSION.
Martin A
13. Why is free water concentration the “driving” force in osmosis?
Free water concentration is the diffusion of water from a lower solute concentration across the membrane to a high solute concentration
-Adam A
14. Why is water balance different for cells that have walls as compared to cells without walls?
A cell w/o a wall is in an isotonic envirornment meaning there will be no net movement of water across the plasma membrane. Water flows across the membrane but at the same rate in both direction. A cell w/ walls is turgid when healthy meaning its very firm w/ alot of water.
-Steph A
15. Label the diagram below:
Lysed Normal Shriveled
Turgid Flaccid Plasmolyzed
a) animal cell fairs best in an isotonic environment unless it has spacial adaptations to offset the osmotic uptake or loss of water
b) plant cells are turgid & generally healthiest in hypotonic environment, where uptake of water is eventually balanced by elastic wall
-Sawyer & Steph, but mostly Sawyer
16. What is the relationship between ion channels, gated channels and facilitated diffusion – write 1 -2 sentences using those terms correctly.
Facilitated diffusion is the phenomenon in which polar molecules and ions can move through the cell membrane with the help of transport proteins. Ion channels and gated channels are two examples of such transporter proteins.
In this image their is a higher concentration of a substance outside of the membrane and it is diffusing through by passive transport. No energy is used just the concentration of substance is enough. It moves through gated and ion channels.
~Ilian D
17. How is ATP specifically used in active transport?
In active transport, energy is needed to transport a molecule across the membrane against the gradient. ATP serves as the source of energy in this process. ATP provides this energy by transferring one of its phosphate groups onto the intracellular side of the transporter protein. Binding of the phosphate causes a conformational change in the protein.
~Ilian D
18. Define and contrast the following terms: membrane potential, electrochemical gradient, electrogenic pump and proton pump.
Membrane potential is the voltage across a membrane, the result of the separation of opposite charges.
Electrochemical gradient is a combination of two forces on an ion: the first one is chemical force (the ion’s concentration gradient), the second one is an electrical force (the result of the membrane potential).
An electrogenic pump is a transport protein that generates voltage across a membrane by transporting more ions in one direction than the other. A proton pump is the most common electrogenic pump in plants, bacteria and fungi, and it is responsible for pumping protons from the inside of the cell to the extracellular environment.
An electrogenic pump generates a membrane potential, and the membrane potential leads to an electrochemical gradient.
~Ilian D
19. What is cotransport and why is an advantage in living systems?
Cotransport is a mechanism in which a single ATP-powered pump that transports a specific solute indirectly drives the active transport of several other solutes. This provides an advantage to living systems because it allows cells to take up critical nutrients such as sugars and amino acids against a concentration gradient. The sugars and amino acids can enter the cell when they ‘hitch’ a ride with a proton.
The hydrogen getting pumped out by ATP causes the transport of hydrogen back into the membrane with the addition of sucrose because sucrose is needed with hydrogen to pump through.
~Ilian D
20. What is a ligand?
A ligand is any molecule that binds specifically to a receptor site of another molecule.
- Laura C
21. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated endocytosis.